1. Field of the Invention
The present invention relates to a holographic data storage medium and an apparatus and method for recording/reproducing data to/from the same, and more particularly, to a holographic data storage medium, which provides discrimination between a plurality of data layers to which data is recorded, and an apparatus and method for recording/reproducing holographic data to/from the same.
2. Description of the Related Art
In recent years, data storage technology using holograms has attracted considerable attention. A method of storing data using holograms includes storing data in the shape of optical interference fringes in inorganic crystals or polymer materials that are sensitive to light. An optical interference fringe is formed by two laser beams with interference. That is, a reference beam and a signal beam with different paths interfere with each other to form an interference fringe that causes chemical or physical changes to a photosensitive storage medium, thus recording data in the photosensitive storage medium. In order to reproduce data from the recorded interference pattern, the reference beam similar to a beam used for recording the data is irradiated to the interference pattern recorded in the photosensitive storage medium. As a result, diffraction occurs due to the interference pattern, so that the signal beam is restored to reproduce the data.
The above-described hologram data storage technology may be divided into a volume holography method in which data is recorded and reproduced in page units using volume holography and a micro-holography method in which data is recorded and reproduced bit by bit using micro-holography. In the volume holography method, a vast amount of data can be processed at the same time; however, it is difficult to make data storage devices commercially available since an optical system should be adjusted very finely.
In the micro-holography method, a signal beam is interfered with a reference beam at a focus to form a fine interference fringe, and a plurality of the fine interference fringe are formed on a plane of a storage medium so that a large amount of data is recorded to form a data layer. The recorded data can be reproduced by irradiating a reference beam to the interference fringe. A volume holographic recording layer is formed so that a plurality of data layers in which data is recorded due to the interference fringe can be formed in a depthwise direction of the volume holographic recording layer. That is, foci of the signal beam and the reference beam are changed in the depthwise direction of the volume holographic recording layer and thus, the plurality of data layers in which data is recorded are formed, thereby three-dimensionally recording data in the volume holographic recording layer.